Understand you are not alone. This is a coral that will challenge the most experienced hobbyist as it can be picky and even get upset from a water change. Goniopora is photosynthetic and gets some of its nutrition from light building zooxanthellae which live in the flesh of the coral which is usually brown in color and regulates the population living in its flesh. Too little light will cause this coral to brown out as in case of yours.
I would not recommend blasting this coral with a lot of light. If you start to see your Goni as in your pic starting to receed , its likely from light intensity being too high and same principle applies to too much flow. If you had a powerhead blowing right at this flowerpot from short range, it may have killed off some of the tissue which caused a domino effect to the rest of the coral piece.
Goni does best in low to medium flow, with some random flow as mentioned above. This will allow a waving motion which helps keep the coral clean and brings food past the colony. If you see its' tentacles thrashing around, there is probably too much flow and reocation to a more calm section of the tank would be best.
Lack of food is a big issue with these coral and there are two types of food you can give them . . . . . Amino acids are one as they play a major role in building proteins as well as other biological functions which corals regularly take in for growth and color. The second type of food is planktonic plankton such as reef chili and reef roids.
The general consensus is to keep Phosphate levels around .05 ppm and Nitrate levels between 10-20 ppm for these guys. This is a safe range for these coral and others especially in a mixed reef.
